This invention relates to a method of simultaneously compacting and freeze-vacuum-dehydrating particulate foods, such as vegetables and meats, so that the dehydrated foods will have substantially greater bulk densities than they do when freeze-vacuum-dehydrated without compaction, and so that upon rehydration the foods will be restored to substantially the same distinct particulate states in which they existed prior to compaction and freeze-vacuum-dehydration thereof.
Freeze-vacuum-dehydration has come to be a frequently applied method of preserving food products as well as a very useful procedure for reducing the weights of foods. It is particularly useful in the production of military rations and components thereof. More recently, since the volume occupied by ration components has been found to be very important both for carrying rations and ration components on the person and for shipping them by air or otherwise, compaction of freeze-dried foods has taken on considerable importance, especially for the Armed Forces. The conventional procedure is to first freeze-vacuum-dehydrate a food and thereafter compact the dehydrated food. If the food is not readily compactible without shattering after being dehydrated, it has been found necessary to plasticize the dehydrated food by adding sufficient moisture or a moisture-mimetic agent to the food and removing the added moisture, in that case, after compaction, or in the case of foods having a fairly high sugar content, by heating the dehydrated food to a temperature sufficiently high to cause plasticization of the food by the heat-softened sugar and compacting the heated, dehydrated food. All of the above-described compaction procedures involve at least two separate steps, namely freeze-vacuum-dehydration and compaction; while in those instances where moisture is employed for plasticization, an additional step of removing the added moisture is usually required since stability of the food in storage may be adversely affected by the added plasticizing moisture, particularly if the average moisture content of the food is increased to more than four percent by weight and remains at such levels after compaction.
It is an object of the present invention to provide a method of producing a compacted freeze-vacuum-dehydrated food of less than about four percent moisture by weight efficiently and economically.
It is another object of the invention to produce a compacted, freeze-vacuum-dehydrated food from a frozen particulate food in a single step rather than in two or more separate steps, the compacted freeze-vacuum-dehydrated food being capable of being rehydrated to a particulate form substantially such as it possessed prior to freezing, compaction, and rehydration.
Other objects and advantages will become apparent from the following description of the invention.